Food size selectivity of Artemia franciscana at three developmental stages

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Abstract
Food size selectivity was examined in Artemia franciscana metanauplii at three different developmental stages. Clearance rates were determined in short-term experiments either by measuring the decrease in concentration of live particles and plastic beads, or by measuring the radioactivity accumulated in animals that grazed 14C-labelled live particles. The maximum clearance rate ofA.franciscana metanauplii increased during development and was measured at 50–63 μl ind.–1 h–1, 254 μl ind.–1 h–1 and 1.48–2.10 ml ind.–1 h–1 in 2-, 4- and 7-day-old metanauplii, respectively. A preference for particles with a diameter of 4–8 μm was observed at all three developmental stages. The ability of A.franciscana metanauplii to graze bacterial particles was also demonstrated, although the efficiency in grazing such small particles was low compared to microalgae (28, 20 and 9% of the maximum clearance rate in 2-, 4- and 7-day-old metanauplii, respectively). Electron microscopy showed that the inter-setular distance in antennae and thoracopods was 0.20 ± 0.07, 0.16 ± 0.05 and 0.18 ± 0.04 μm in 2-, 4- and 7-day-old metanauplii, respectively, and accordingly independent of stage.

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